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SITE BULLETIN, ATTENUATED ANAEROBIC DECHLORINATION OF GROUNDWATER USING HRC MACTEC - HARDING ESE
Citation:
de Percin*, P R. SITE BULLETIN, ATTENUATED ANAEROBIC DECHLORINATION OF GROUNDWATER USING HRC MACTEC - HARDING ESE. U.S. Environmental Protection Agency, Washington, DC, EPA/540/R-08/003, 2008.
Impact/Purpose:
To determine the effectiveness of the permeable reactive barrier wall in eliminating TCE and its degradation products from the groundwater plume.
Description:
A SITE demonstration of the Harding ESE permeable reactive barrier wall (PRBW) was conducted on the contaminated groundwater from the Fisherville Mill site in Grafton, MA beginning June 2000 to July 2003. Installation of the PRBW was accomplished by injecting HRC into a series of wells downgradient of an existing monitoring well and further installing wells further downgradient to monitor the impact of the PRBW. The injection wells were spaced in order to provide overlap of HRC when injected into the aquifer at 40-50 feet below ground surface (bgs) perpendicular to the groundwater flow. The areal extent of the pilot-scale treatment system's injection and monitoring wells was approximately 1,200 ft2. Two rows of monitoring wells were installed for tracking HRC and contaminated groundwater movement. The first row was installed 12-15 feet south of the PRBW and the second row was installed about 30 feet south. The two rows of wells allowed the monitoring of HRC effectiveness as it moved with the groundwater. There were lateral wells to determine if the HRC injection interfered with the groundwater flow, i.e., if the groundwater flowed around the wall.
The primary objective of the demonstration was to determine the effectiveness of the PRBW in eliminating TCE and its degradation products from the groundwater plume. Specifically, the developer claimed that 90% of the water samples collected from the downgradient "critical" wells would meet the Massachusetts groundwater criteria (GW-1), after a reasonable period of time (about 4 months). GW-1 criteria for the target contaminants are as follows: TCE (5 ppb), cis and trans-1,2-dichloroethene (70 ppb-combined), and vinyl chloride (2 ppb).
The demonstration was initially expected to last about 6 to 9 months, which was anticipated to be ample time for determining if the primary objective had been met. In fact, the demonstration was extended to over 24 months as TCE concentrations were found to decrease more slowly than expected. Water level measurements indicated the project area was very flat. Although this would suggest low water flow, analysis of various parameters indicated that movement of HRC was occurring. Concentrations of VOCs and other parameters varied in adjacent wells throughout the evaluation, possibly due to non-uniformity in the formation; nevertheless each well showed similar trends in VOC changes.
After a few months of contact with HRC there was clear evidence of conversion of TCE to cis-1 ,2-DCE. Although the treatment did achieve extensive conversation to DCE, the GW-1 criteria were not achieved even after two years.
URLs/Downloads:
SITE Bulletin, Attentuated Anaerobic Dechlorination Of Groundwater Using HRC Matec-Harding ESE (PDF, NA pp, 119 KB, about PDF)SITE BULLETIN, ATTENUATED ANAEROBIC DECHLORINATION OF GROUNDWATER USING HRC MACTEC - HARDING ESE